The OP later edited his question and included more broken examples, one for colortbl itself, the other for xcolor.

It is now possible to use the following commands:

\definecolor{Blue}{rgb}{0,.6,1}
\begin{tabular}{ >{\color[named]{Blue}} cc}
Blue&White\\
Blue&White
\end{tabular}

\begin{tabular}{ >{\color[rgb]{0,.6,1}} cc}
Blue&White\\
Blue&White
\end{tabular}

With xcolor, it is now possible to use colors defined in the preamble:

\documentclass{article}
\usepackage{xcolor}
\definecolor{Blue}{rgb}{0,.6,1}
\begin{document}
\textcolor{Blue}{Blue---I don't think so.}
\textcolor{red!72.75}{Red text}
\textcolor{.!50}{Gray text}
\textcolor{Blue}{Blue again}

\end{document}

An user submitted an issue on TeX.sx [1]:

------------
\documentclass{article}
\usepackage[table]{xcolor}
\begin{document}

\begin{tabular}{ >{\columncolor[rgb]{0,.6,1}} cc}
Blue&White\\
Blue&White
\end{tabular}
\end{document}
-----------

It crashes because current tex4ht configuration for columncolor expects the color components to be separated by spaces, instead of commas, which are actually used by color and xcolor packages. I've modified the colortbl.4ht to load the xcolor.sty package, colortbl.sty loads color.sty by default. )

xcolor.sty provides commands for color space conversion, so it is no longer needed to use special configurations in colortbl.4ht, which were used for rgb, gray and cmyk colorspaces. The new version is simpler and as a bonus it supports more color spaces than the original version.

We probably should revisit color support in tex4ht someday, but we already found quite a bit issues in the last month, so it doesn't have much high priority right now, I guess.

[1] http://tex.stackexchange.com/q/343773/2891